I am using a 35k mile interval with mine. Mazda does not mention a recommended change interval so we are all on our own with this. Old wives' tales are the order of the day here, but with a good dose of practicality in most cases. I don't think you would be hurting anything by changing at 10k, but I'm sure extending that interval to twice or three times as long would be perfectly fine as well. In fact, I don't think changing at 50k would be problematic either. I'll be tackling this again in a few days (hopefully) as I will be reaching 35k since my last change in February last year. I've already obtained the fluid from rockauto.com and this time I got the Idemitsu brand.
My last change I got the Beck/Arnley brand which is still available, but is a wee bit more expensive ($6.20 vs $6.79).
Idemitsu is the OEM for Mazda's fluid so I'll be using that for now, as long as it's available. B/A will be my fall-back.